Rock Adagio is an electric flute composition that developed in many versions from 1992 to 2011. They all include a re-composition of J.S.Bach's Adagio from Flute Sonata No.4 in C Major, BWV 1033. (Attributed to JSBach; suspected to be a work of C.P.E. Bach.)
This is the score of the first version that starts with the Bach Adagio and leads up to the improvisation section. The 1992 recording of this version is 3min 30sec.